Alright, I just want to say that I think not having kids is selfish, BUT I would also say that having kids is selfish as well. I think both choices, whether you choose kids or no kids has a small amount of selfishness in them. Think about it, people generally have kids because they want them. They want all the "cute" things that come along and they want recognition as being a parent. Also, people who don't have kids often choose not to have them so they can focus more on their career or each other and so their money can go to things they think will make their lives more enjoyable.
I also think that whether you choose to have kids or not, this choice can be seen as selfless. For example if you choose not to have kids it may be because you don't feel you can give a child the a good life or be a good parent/guardian to them. You may choose not to have kids because you want to give them opportunities that you may not be able to give them due to money or other issues. In contrast it can be selfless to have kids because you are putting someones life before your own, devoting much of your time an money into raising a human being.
I think that it is wrong for somone who has kids to say that someone is selfish for deciding not to have children. Maybe that couple did TRY to have kids, but couldn't. Maybe there are other issues that no one knows about the couple. I think it's also important that people who do not have kids realize that simply because they made the choice not to have kids, doesn't make their life any better or worse. I guess what I am trying to say, is someday we have to realize that everyone is different. How one persons perceives something is entirely different from another. I think that when we finally can do this we will avoid this lame internet thread bashing about who is right and wrong.
I think that it is also important that we DO question. Maybe ask a couple, Did you ever think of having children? Why or why not? etc. and that the ones be questioned not take it personally and remind themselves that this person may just be curious.
I'll step down from my soap box now....